首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   2777篇
  免费   181篇
林业   237篇
农学   117篇
基础科学   37篇
  663篇
综合类   116篇
农作物   182篇
水产渔业   351篇
畜牧兽医   1004篇
园艺   61篇
植物保护   190篇
  2023年   22篇
  2022年   69篇
  2021年   131篇
  2020年   114篇
  2019年   130篇
  2018年   101篇
  2017年   116篇
  2016年   118篇
  2015年   101篇
  2014年   144篇
  2013年   205篇
  2012年   223篇
  2011年   241篇
  2010年   132篇
  2009年   135篇
  2008年   137篇
  2007年   164篇
  2006年   115篇
  2005年   101篇
  2004年   98篇
  2003年   97篇
  2002年   66篇
  2001年   19篇
  2000年   15篇
  1999年   16篇
  1998年   17篇
  1997年   11篇
  1996年   7篇
  1995年   5篇
  1994年   7篇
  1993年   8篇
  1992年   11篇
  1991年   5篇
  1990年   4篇
  1989年   6篇
  1988年   4篇
  1987年   8篇
  1986年   3篇
  1985年   5篇
  1984年   5篇
  1983年   3篇
  1982年   3篇
  1981年   4篇
  1980年   5篇
  1976年   3篇
  1975年   3篇
  1973年   3篇
  1972年   4篇
  1969年   2篇
  1966年   2篇
排序方式: 共有2958条查询结果,搜索用时 671 毫秒
991.
992.
993.
Journal of Crop Science and Biotechnology - The rhizobacteria of genus Azospirillum and Bacillus are effective at fixing atmospheric nitrogen, promote plant growth and can largely contribute to...  相似文献   
994.
Naturally occurring biological entities with extractable and tunable structural and functional characteristics, along with therapeutic attributes, are of supreme interest for strengthening the twenty-first-century biomedical settings. Irrespective of ongoing technological and clinical advancement, traditional medicinal practices to address and manage inflammatory bowel disease (IBD) are inefficient and the effect of the administered therapeutic cues is limited. The reasonable immune response or invasion should also be circumvented for successful clinical translation of engineered cues as highly efficient and robust bioactive entities. In this context, research is underway worldwide, and researchers have redirected or regained their interests in valorizing the naturally occurring biological entities/resources, for example, algal biome so-called “treasure of untouched or underexploited sources”. Algal biome from the marine environment is an immense source of excellence that has also been demonstrated as a source of bioactive compounds with unique chemical, structural, and functional features. Moreover, the molecular modeling and synthesis of new drugs based on marine-derived therapeutic and biological cues can show greater efficacy and specificity for the therapeutics. Herein, an effort has been made to cover the existing literature gap on the exploitation of naturally occurring biological entities/resources to address and efficiently manage IBD. Following a brief background study, a focus was given to design characteristics, performance evaluation of engineered cues, and point-of-care IBD therapeutics of diverse bioactive compounds from the algal biome. Noteworthy potentialities of marine-derived biologically active compounds have also been spotlighted to underlying the impact role of bio-active elements with the related pathways. The current review is also focused on the applied standpoint and clinical translation of marine-derived bioactive compounds. Furthermore, a detailed overview of clinical applications and future perspectives are also given in this review.  相似文献   
995.
Three dermacozines, dermacozines N–P (1–3), were isolated from the piezotolerant Actinomycete strain Dermacoccus abyssi MT 1.1T, which was isolated from a Mariana Trench sediment in 2006. Herein, we report the elucidation of their structures using a combination of 1D/2D NMR, LC-HRESI-MSn, UV–Visible, and IR spectroscopy. Further confirmation of the structures was achieved through the analysis of data from density functional theory (DFT)–UV–Visible spectral calculations and statistical analysis such as two tailed t-test, linear regression-, and multiple linear regression analysis applied to either solely experimental or to experimental and calculated 13C-NMR chemical shift data. Dermacozine N (1) bears a novel linear pentacyclic phenoxazine framework that has never been reported as a natural product. Dermacozine O (2) is a constitutional isomer of the known dermacozine F while dermacozine P (3) is 8-benzoyl-6-carbamoylphenazine-1-carboxylic acid. Dermacozine N (1) is unique among phenoxazines due to its near infrared (NIR) absorption maxima, which would make this compound an excellent candidate for research in biosensing chemistry, photodynamic therapy (PDT), opto-electronic applications, and metabolic mapping at the cellular level. Furthermore, dermacozine N (1) possesses weak cytotoxic activity against melanoma (A2058) and hepatocellular carcinoma cells (HepG2) with IC50 values of 51 and 38 μM, respectively.  相似文献   
996.
The antioxidant capacity as oxygen radical absorbance capacity (ORAC) and in vitro chemopreventive effect of phytochemicals extracted, partitioned and isolated from the decorticated bran of black Shawaya sorghum (Sorghum bicolor L. Moench) was studied. The chemopreventive effect was evaluated as the induction effect of quinone reductase (QR) using murine hepatoma cells Hepa 1c1c7. The crude methanol extract with an antioxidant capacity of 3.7 μmol Trolox equivalent (TE)/mg was partitioned into 120 fractions with fast centrifugal partition chromatography (FCPC). Fractions with partition coefficients between 0.1 and 0.26 exerted more than 50% of the antioxidant activity of the original crude extract and contained the highest concentration of anthocyanins. No correlation was found for ferulic acid content and ORAC or chemoprevention. A derivative of 7-methoxyapigeninidin at a concentration of 1 μg/ml increased by 31% the QR activity while the original extract reached a maximum of 27% at 40 μg/ml.  相似文献   
997.
The effects of four different ionic composition low salinity water (T1, T2, T3, and T4), on growth and survival of Litopenaeus vannamei marine shrimp juveniles were investigated. Shrimp culture in seawater (Tm) was used as control treatment. The results indicated that there were no significant difference (P < 0.05) in growth, survival, production, and feed conversion ratio (FCR) of L. vannamei juveniles reared in the different treatments, but significant differences (P < 0.05) were observed between each of them when compared with seawater (Tm). After 84 days, culture shrimp grew from 0.02 to 7.58 g in T1. The lowest growth rate was attained in T3 (0.57 g/week), in which potassium and calcium ions concentrations were the lowest (0.58 and 28.00 mg/L, respectively). The recorded survival rate (76.35% to 79.55%) is considered well for the 84 days growout period, although it was 7.6% lower than that recorded in the control treatment. Although there were no significant differences (P < 0.05) in growth with respect to the ionic composition of the four treatments, there was a trend of increasing growth in relation with the ionic ratio found in the seawater (Tm). This aspect should be evaluated more closely in future research.  相似文献   
998.
The pink shrimp Farfantepenaeus brasiliensis is native in southern Brazil and is potentially suited for aquaculture. Under intensive culture, the accumulation of nitrogenous compounds results from excretion by the shrimp and from the processes of feed decomposition and nitrification. The objective of this study was to evaluate ammonia, nitrite, and nitrate toxicity effects on oxygen consumption of juvenile pink shrimp. Shrimps (initial weight 0.7 ± 0.15 g) were exposed over a period of 30 days to 50%, 100%, and 200% of the safe levels of total ammonia (TAN = 0.88 mg/L), nitrite (NO2? = 10.59 mg/L), and nitrate (NO3? = 91.20 mg/L) for the species. The specimens were individually collected and placed in respirometry chambers, where the oxygen consumption was measured over a period of two hours. Throughout the experiment there was no significant difference (p > 0.05) among treatments in terms of survival and growth. The pink shrimp juveniles exposed to nitrogen concentrations of 200% of the nitrite and nitrate safe level showed the highest oxygen consumption (p < 0.05).  相似文献   
999.
We analyzed the effect of commercial bacterial probiotics on a Litopenaeus vannamei biofloc culture system infected with Vibrio parahaemolyticus. Three replicates of two experimental treatments were conducted: a control system (without probiotic) and a system with the application of a multistrain probiotic containing Bacillus spp., Enterococcus spp., Thiobacillus spp., and Paracoccus spp. applied to the water and another multistrain probiotic containing Bacillus spp., Enterococcus spp., and Lactobacillus spp. added to the feed. Growth and survival rate were significantly higher in the probiotic treatment group (P < 0.05), and the shrimp in the probiotic group also had a lower (P < 0.05) FCR compared to the shrimp in the control group (1.4 vs. 2.7).  相似文献   
1000.
Stable isotope analyses were applied to explore the relative dietary nitrogen contributions from fish meal and pea meal (Pisum sativum) to muscle tissue of Pacific white shrimp postlarvae (141 ± 31 mg) fed low protein diets having different proportions of both ingredients as the sole dietary protein sources. A negative control diet was formulated to contain 100% pea meal and six more isoproteic diets to have decreasing levels of pea meal‐derived nitrogen: 95%, 85%, 70%, 55%, 40% and 0% of the initial level. Growth rates were negatively correlated to dietary pea protein inclusion due to progressive essential amino acid deficiencies (sulphur amino acids, threonine, lysine, histidine). The nitrogen turnover rate significantly increased in muscle tissue of shrimps fed diets having high levels of pea meal; however, contrary to observations from a previous study using soy protein, the relative contributions of dietary nitrogen from pea meal to shrimp muscle tissue were equal or higher than expected contributions established by the dietary formulations. Results highlight the effectiveness of stable isotope analysis in assessing the nutritional contributions of alternative ingredients for aquaculture feeds and the potential suitability of pea as a source of protein (provided the diets are nutritionally balanced).  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号